1. Field of the Invention
The present invention relates to an image quality adjuster circuit which adjusts an image quality on a flat panel such as a liquid crystal display or a plasma display and on a CRT display, and more particularly, to a video signal processor circuit which adjusts a contrast and a television receiver.
2. Description of the Related Art
In particular, a flat panel such as a liquid crystal display or a plasma display has a narrow input dynamic range because of its characteristics. In order to efficiently utilize the narrow dynamic range, a dynamic contrast (Y-γ) correcting circuit for arbitrary setting a level of expanding a signal amplitude in response to an input signal state is used.
Conventionally, in one of known Y-γ correcting methods, IRE levels of arbitrary two points are preset, and image quality adjustment is made while a dark portion and a bright portion are distinguished from each other around the set levels. The IRE (Institute of Radio Engineers) level denotes a unit when a pedestal level (reference level) is defined as 0% and a complete while level is defined as 100%.
For example, in a dark scene, the IRE levels of the two points are highly set as compared with a case of a flat characteristic, whereby the amplitude of an input signal at the dark portion is expanded. In a scene having intermediate brightness, the IRE level at the dark portion side is lowly set, and the IRE level at the bright portion side is highly set, as compared with the case of the flat characteristic.
Consequently, the amplitude of the input signal at the dark portion is reduced, and the amplitude of the input signal at the bright portion is expanded. Further, in a bright scene, the IRE levels of the two points are lowly set as compared with the flat characteristic, whereby the amplitude of the input signal at the bright portion is expanded.
However, the above-described conventional Y-γ correcting method makes contrast adjustment by changing the settings of the IRE levels of the two points. Thus, there is inconvenience that optimal adjustment cannot be made for a variety of input signals.